GB1338256A - Battery powered circuits - Google Patents

Abstract

1338256 Battery charging and testing circuits EMI Ltd 19 April 1971 [17 April 1970] 18348/70 Heading H2H [Also in Division G1] A battery powered circuit includes sampling means for taking current pulses from the battery at predetermined intervals and sensing means which provide a warning signal in response to a predetermined drop in the battery voltage when supplying the current pulses. The circuit is also provided with means for recharging the battery and the charging current may be controlled in dependence upon the battery voltage. A battery (not shown) is connected to terminals 48, 49 so as to be chargeable from an A.C. supply 1, 2 by way of a rectifier 3 and lines 7, 6; a parallel pair of transistors 12, 13 being connected in the line 6. The transistors 12, 13 are controlled such that the charging current is substantially constant, the control being effected by zener diodes 9, 10, 11 and a transistor 8, the charging current value being selectable by a potentiometer 16. When the battery voltage reaches a required level a transistor 17 is turned on, the level being determined by a potentiometer 19. Turning on of transistor 17 causes the transistor 8 to reduce the flow of current through the transistors 12, 13 to a trickle charge value. A meter 20 is provided to indicate the charging current or, either the battery voltage or the charging voltage, according to the position of a switch 21. The circuit is protected from a wrongly connected battery by a diode 24 and fuse 25. The sampling means for taking current pulses from the battery includes a unijunction transistor 26 and a thyristor 29. The transistor 26 is arranged in the mode of an astable multivibrator which provides an output pulse every minute. The output pulse is applied to the thyristor 29 to render it conductive which then renders an emitter following transistor 27 conductive, whereupon a transistor 28 is also made conductive. The elements 29, 27, 28 thus connect resistors 30, 31, 32 across the battery so that the battery supplies a discharge pulse therethrough the pulse being terminated when a capacitor 33 receives a predetermined charge. The battery voltage sensing means includes a unijunction transistor 34 which becomes conductive should a negative-going pulse of sufficient magnitude to indicate a deterioration in the battery condition be received at the upper base of the transistor 34 when a current pulse is taken from the battery by resistors 30, 31, 32. When the transistor 34 conducts, a capacitor 36 discharges through a resistor 37, thus to trigger a thyristor 38 to short-circuit a relay 39. Contact 40 of the relay then assumes the position indicated in the Figure, thus providing a "fault" indication on terminal 43 and illuminating a lamp 41. At the same time a contact 44 moves to the position shown to disconnect the sampling circuit from the battery to prevent further drain thereon. The circuit can be reset by means of a manually operable switch 45 which turns off the thyristor 38, a signal on a terminal 47 indicating a satisfactory reset. The sensitivity of the sensing means is set by a potentiometer 35. A fuse 46 is provided to prevent damage to the sampling and sensing circuits should a fault occur in the battery testing circuit.